Further, we crop CT images to a bounding box of the lungs mask. We obtain the latter mask by training a standalone CNN segmentation model. The training procedure and architecture are reproduced from [1]}. The training of the lung segmentation model involves two external chest CT datasets: LUNA16 [2]}, [3]} and NSCLC-Radiomics [4]}, [5]}. These datasets have an empty intersection with the other datasets used to train the COVID-19 segmentation models; thus, there is no leak of the test data.
